Fixed the cc65 code that optimizes 16-bit compares when the high bytes are known to be equal.

Only the low bytes are compared. Originally, signed 16-bit compares were optimized into signed 8-bit compares. But, the sign bits are in the high bytes; and, they're equal. Therefore, the low bytes always must be compared as unsigned numbers. Fixes #1348.
2020-12-24 12:27:09 -05:00
parent 0f4cb443b4
commit b2c1a77bb3
3 changed files with 37 additions and 77 deletions
--- a/test/val/bug1348.c
+++ b/test/val/bug1348.c
@@ -0,0 +1,54 @@
+/* bug #1348, wrongly optimized integer promotion in comparison */
+
+#include <stdio.h>
+
+static const int notrandtab[] = {
+    0xffff, 0x7fff, 0x3fff, 0x1fff,
+    0x0fff, 0x07ff, 0x03ff, 0x01ff,
+    0x00ff, 0x007f, 0x003f, 0x001f,
+    0x000f, 0x0007, 0x0003, 0x0001
+};
+
+static unsigned char notrandcount = 0;
+
+static int notrand(void)
+{
+    return notrandtab[notrandcount & 0x0f];
+}
+
+static unsigned char n1, n2;
+static unsigned char i, ii, s;
+static unsigned char err = 0;
+
+static const unsigned char cmptab[] = {
+    0xff, 0x7f, 0x3f, 0x1f,
+    0x0f, 0x07, 0x03, 0x01,
+    0x80, 0x40, 0x20, 0x10,
+    0x08, 0x04, 0x02, 0x01
+};
+
+int main(void)
+{
+    for (ii = 0; ii < 16; ++ii) {
+        s = cmptab[ii];
+        for (i = 0; i < 16; ++i) {
+            n1 = n2 = 0;
+            if ((notrand() & 0xff) > s) {
+                n1 = 1;
+            }
+            if ((notrand() & 0xffu) > s) {
+                n2 = 1;
+            }
+            printf("%5d > %3d %u(%02x) %u(%02x)  %s\n",
+                   notrandtab[i], s,
+                   n1, (notrand() & 0xff),
+                   n2, (notrand() & 0xffu),
+                   n1 == n2 ? "=" : "!=");
+            if (n1 != n2) {
+                err = 1;
+            }
+            notrandcount++;
+        }
+    }
+    return err;
+}